The present invention pertains generally to molding methods for sensitive members, such as electrical elements, and more particularly to leadframe structures for retaining components in proper position on the leadframe prior to a premolding and/or an overmolding process, so that the component can be included in the premold or overmold.
In various industries, it is known to provide non-plastic components imbedded in plastic bodies, to increase durability and performance of the components. For example, it is known to provide various electrical components embedded in plastic, with contact portions thereof extending outwardly of the plastic body, to connect to an electrical circuit. By exposing only the necessary contacts, the remaining embedded portions of the component can be protected from harsh ambient conditions, from physical contact that could result in damage, from jarring that may impair proper function, or other undesirable exterior conditions.
A known process to provide electrical components embedded in plastic includes the formation of a leadframe of conductive metal, the formation of a premold over some parts of the leadframe, and the subsequent formation of an overmold over some or all of the leadframe, and over some or all of the premold.
The leadframe includes a central frame of permanent components in the finished product, and may further include an outer frame or hoop to stabilize the central frame during premolding and/or overmolding processes. Parts of the outer frame are removed after premolding and/or overmolding.
Premolding/overmolding processes as described above are used to protect sensitive elements from ambient conditions and to prevent contamination or damage during use. In the manufacture of some products, it is necessary to provide various other components separately attached or connected to the leadframe. Advantages can be obtained for some such assemblies if the component can be assembled on the leadframe prior to premolding or overmolding, so that the component can be encapsulated as well, during the premolding and/or overmolding processes. However, doing so is not without difficulties, as the component must be secured in position relative to the leadframe. If the component is positioned improperly, failure of the molding process and/or the resulting molded part can result.
Retaining a component properly positioned on a leadframe can be achieved with stops, lands or holding devices in the mold, but the use of such can result in a non-hermetic seal around the component. It also can be more difficult to assemble and position the components in the mold, making manufacture more difficult. Assembling the component on the leadframe when the leadframe is positioned in the mold can be awkward and time consuming, slowing the molding process. If the component is merely placed on the leadframe in advance of sending the leadframe to the molding step, the component can become displaced on the leadframe, separated from the leadframe or lost entirely.
What is needed in the art is a structure integral with the leadframe, for retaining components in proper position on the leadframe prior to a premolding and/or an overmolding process.
The present invention provides a leadframe structure that secures components thereon, to maintain the position of the component on the leadframe during a premolding and/or overmolding process. The structure allows pre-assembly of the leadframe with the component, thereby facilitating subsequent premolding and/or overmolding processes
In one aspect thereof, the invention provides a leadframe with a central frame and at least one component receiving projection from the central frame. A biasing member is associated with the component receiving projection, adapted and arranged to operate on a component installed on the component receiving projection. A locking means is associated with the biasing member to inhibit movement of the component on the component receiving projection under biasing influence of the biasing member.
In another aspect of the invention, a leadframe assembly is provided with a leadframe including a central frame, and at least one component receiving projection from the central frame. A component is installed over the component receiving projection. A biasing member associated with the component receiving projection is adapted and arranged to operate on the component installed on the component receiving projection. A locking means associated with the biasing member inhibits movement of the component on the component receiving projection under biasing influence of the biasing member.
In still another aspect thereof, the invention provides a leadframe assembly with a leadframe including a central frame, an outer frame at least partially surrounding the central frame and connected to the central frame by at least one bridge for reinforcing the central frame, and at least one electrical contact projecting outwardly from the central frame. The contact is a monolithic structure having a base and a biasing member overlying the base. The biasing member is connected to the base along distal segments thereof, and is formed to overlie the base along a fold. The biasing member has a proximal segment free from the base, and a protuberance extending laterally of the base. A shoulder is formed at an end of the fold, disposed laterally beyond an edge of the base. A ferrite noise filter is installed over the contact, the filter having a hole minimally larger than the contact. The filter is disposed on the contact between the central frame and the shoulder. The protuberance and the proximal segment of the biasing member bias the filter to maintain positioning of the filter between the shoulder and the central frame.
An advantage of the present invention is providing a leadframe structure with an additional component thereon, facilitating subsequent premolding and/or overmolding processes by ensuring proper positioning of the component on the leadframe.
Another advantage of the present invention is providing a leadframe assembly with a component mounted and secured thereon, allowing encapsulation of the component during premolding and/or overmolding.
A further advantage of the present invention is providing a leadframe assembly with a noise filter on electrical contacts of the leadframe, with plastic encapsulating the filter and selected portions of the leadframe.